Rollup merge of #121382 - nnethercote:rework-untranslatable_diagnostic-lint, r=davidtwco

Rework `untranslatable_diagnostic` lint

Currently it only checks calls to functions marked with `#[rustc_lint_diagnostics]`. This PR changes it to check calls to any function with an `impl Into<{D,Subd}iagnosticMessage>` parameter. This greatly improves its coverage and doesn't rely on people remembering to add `#[rustc_lint_diagnostics]`. It also lets us add `#[rustc_lint_diagnostics]` to a number of functions that don't have an `impl Into<{D,Subd}iagnosticMessage>`, such as `Diag::span`.

r? ``@davidtwco``

compiler/rustc_session/src/session.rs

@@ -312,6 +312,7 @@ impl Session {
     ) -> Diag<'a> {
         let mut err = self.dcx().create_err(err);
         if err.code.is_none() {
+            #[allow(rustc::diagnostic_outside_of_impl)]
             err.code(E0658);
         }
         add_feature_diagnostics(&mut err, self, feature);
@@ -1022,6 +1023,7 @@ fn default_emitter(
 
 // JUSTIFICATION: literally session construction
 #[allow(rustc::bad_opt_access)]
+#[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
 pub fn build_session(
     early_dcx: EarlyDiagCtxt,
     sopts: config::Options,